Liquid crystal devices employing electro-optical materials that vary their transmissivity in response to an applied electrical potential are commonly used in visual displays of information in applications such as computers, televisions, calculators, radios, automobile controls, and many other products. While display devices embodying these principles are well known, problems with the manufacture of such devices are also well known. One problem that occurs when liquid crystal displays (LCDs) are made thin (in order to achieve low voltage operation) is short circuits appearing across the fluid layer. Another problem is the difficulty in providing consistency of the gap between the two electrodes in the LCD. Since the performance of the device is a function of the consistency of the gap, it is important to accurately control this spacing for maximum uniformity. Unevenness in the spacing produces poor optical properties and promotes rapid deterioration of the liquid crystal fluid. Because of these and other problems, the manufacture of reliable, long-life liquid crystal displays has been difficult.
During the manufacture of LCDs, small spheres are typically applied to a glass substrate to serve as spacers. These spheres perform the function of precisely setting the gap between the upper and lower substrates, the gap being subsequently filled with the liquid crystal fluid. The spheres must be applied in a uniform manner to prevent the substrates from bowing and in order to maintain a uniform gap. Uniform dispersion of the spheres is also required in order to achieve the proper display contrast and performance. Typically, spacer spheres are applied to the substrate by spraying on a suspension of the spheres in a chlorofluorocarbon solvent (CFC). The recent global banning of all CFC usage will soon impact the processes used to manufacture LCDs and an alternative technique is required. Some of these alternative techniques being evaluated by the industry are spraying the spheres using water-based suspensions. Spraying from these types of suspensions does not yield uniform spacer placement on the substrates. Electrostatic spraying has been used with good results reported in the literature. However, electrostatic systems remain unproved in production use and are very expensive.
In addition, existing methods of applying the spacers are not adequate where a high number of spacers per unit area (for example, greater than 20 spacers per square millimeter) of the display is required, such as in large area displays. Current methods result in spacer clumping or aggregation when the spacers are applied in high densities. Clearly, an alternative, low-cost method of applying the spacers onto the substrate would be desirable. Such a method should avoid the use of CFCs and also result in a high-quality LCD.